The present invention relates to injection devices and, in particular, to a device for the intramuscular or subcutaneous injection of a pharmaceutically active compound.
The parenteral introduction of pharmaceutically active compounds is preferred over oral dosage in many applications. For example, when the drug to be administered would partially or totally degrade in the gastrointestinal tract, parenteral administration is preferred. Similarly, where there is need for rapid response in emergency cases, parenteral administration is preferred over oral administration.
Thus, while parenteral administration is desirable in many applications, as it is currently practiced it has substantial drawbacks. Probably the biggest drawback is the discomfort which it causes the patient to whom the drug is being administered. Parenteral preparations generally contain a large volume of liquid in which the drug is suspended or dissolved. Ratios of active ingredient to carrier commonly run from 1:100 to 1:1000. When the active ingredient is poorly soluble or difficult to suspend in the carrier, or when the active ingredient has to be administered at high doses, or in both instances, a fairly large volume of liquid must be injected. Both the size of the needle and the volume of liquid being injected cause parenteral administration to be more or less painful, and at least disagreeable, for most people. Furthermore, depending on its nature, the carrier itself may be a cause of pain.
A further disadvantage to administration of drugs in a liquid carrier is that the drugs are frequently not stable in the liquid. Therefore, the liquid and drug must be mixed substantially contemporaneously with injection. This can be of substantial disadvantage where, for example, many hundreds of people must be treated over a course of days in order to stem an epidemic.
Drugs in solid form rather than liquid form have been used for prolonged or controlled release formulations. When the formulation is not a microstructure or a powder that can be injected in suspension form, with a liquid and a standard syringe, the formulation is usually an implant or a rod which can be injected directly via a trocar, see for example European Patent Application Publication No. 0292936. However, trocars and the device as set forth in the cited European Patent have some disadvantages. When the formulation is a prolonged or controlled formulation, the formulation must contain the daily dose of drug multiplied by the number of days of activity of the drug and the amount of carrier necessary to control the rate of delivery of that drug. Thus this formulation, which is in the needle, requires a needle significantly larger than ordinary needles used with syringes and this results in a painful injection.